Means for igniting an igniter primer



United States Patent 3,124,075 MEANS FOR IGNITING AN IGNITER PRIMER John Alex Dorge Eldh, Backaskiftsvagen 68, Enskede, Sweden, and Gtista Vilhelm Gustafsson, Satravagen 62, Hagersten, Sweden Filed Oct. 9, 1961, Ser. No. 143,707 8 Claims. (Cl. 102-865) This invention relates to means for the initiation of igniter primers by means of a pin or the like.

The development and improvement of initiating means such as primers, primer cartridges and percussion caps, both for ammunition and other uses have caused a demand for increased sensitivity of the initiating explosives in order to ensure proper functioning. When the initiation is effected by a pin entering the ignition charge the actual detonation of the ignition is caused by the development of heat due to the friction between the pin and the ignition charge. The sensitivity of ignition charges can be increased by mixing with frictional material such as ground glass or calcium silicide or the friction sensitivity can be increased by the addition of a suitable explosive, e.g. tetrazine. However, these two types of additions act as diluents and reduce the brisance or strength of the ignition charge.

Moreover, an increased sensitivity to friction causes safety problems in manufacture. Therefore an extreme reduction of the impact energy necessary to cause detonation by altering the composition of the ignition charge is entailed with great practical diificulties such as trouble in handling.

With conventional impinging-type initiating devices the form of the pin (point angle) and the nature of its engaging surface are of considerable importance for the development of the energy needed to cause detonation or deflagration when the pin penetrates the ignition charge.

In order to keep the sensitivity and other qualities of initiation means constant in mass production, it is therefore necessary to enforce a strict control over the accuracy of the pins and their surface finish. It is also necessary to prevent corrosion of the pins during storage and transport. As a result, production costs are considerable.

The present invention relates to improvements in initiating means of the impinging type. One object of the improvements is to achieve absolute safety in handling and proper function in operation. A further object of the new initiating means is to reduce the energy necessary to cause initiation and to reduce misfires. The adoption of this new feature enables the tolerances in manufacturing the pin to be increased. Another improvement in the initiating means (described in full detail below) consists in pressing the charge as a layer onto an anvil of hard material. The pin penetrates this layer and strikes the anvil.

One technical advantage gained with initiating means embodying the invention is that the percussive effect of the pin against the anvil is used to cause the initial detonation or defiagration so that the thin layer of ignition charge can always be detonated even though it is not of a highly sensitive class. Therefore the device is safe to handle though its effective sensitivity is high.

The use of a thin layer of ignition charge on the anvil enables the speed of the ignition to be increased as the path of the pin is short and the kinetic energy lost through penetration of the layer of ignition charge is small. There is a correlation between effective initiation time and the thickness of the layer; i.e. if the layer is of constant thickness in a number of initiating means the detonation time will also be constant. Thus, the initiation time can be varied between certain limits by varying the thickness of 3,124,075 Patented Mar. 10, 1964 the layer of the ignition charge, on the anvil. The ignition charge layer can, if desired, be free of inert friction material and of highly friction-sensitive explosives. The deflagration or detonation in the initiating means that is, in the thin layer quickly attains its full velocity, i.e. there is good acceleration. The novel initiating means e.g. in the form of a percussion cap is more effective than conventional caps of greater volume in which the initial explosion takes place at a certain depth within the explosive instead of on its surface.

According to one embodiment of the novel initiating means no metal parts are used so that the means is especially useful for anti-tank mines.

Owing to the decreased impact energy necessary i.e. increased sensitivity, the novel initiating means are suitable for impact fuses for shells designed to burst on impact on the ground.

The improvements also make special primer cartridges unnecessary.

Two novel initiating means are now described for example with reference to the accompanying diagrammatic drawing.

FIGURE 1 shows the percussion cap and a mine primer in axial section.

FIGURE 2 shows another percussion cap for a primer in axial section.

The percussion caps of FIGS. 1 and 2 are detonated by a pin 2 and comprise a metallic or a non-metallic capsule 1. The latter contains a secondary or main explosive 5, pressed into the capsule, such as tetryl or trotyl and an ignition charge 4, 4a and priming charge 4b such as dextrinated lead azide, or mercury fulminate. The free surface of the ignition charge 4, 4a is covered by a protecting metallic or non-metallic foil 6 such as a thin aluminum or polythene foil.

' In the embodiment of FIGURE 1, the capsule is partly sealed by a frontal cover 7 having a central aperture. The ignition charge 4 is arranged adjacent to the main charge 5. Arranged in the path of the pin 2 there is an anvil 3 of hard metal, between the charges 4 and 5. There is only a thin layer of the ignition charge covering the face of the anvil facing the pin. The thickness of the layer may, for instance be about 0.5 mm. The anvil can be cylindrical or cubical in form, for instance, and can have a thickness of, for instance, 1 mm. In order to avoid displacement of the anvil 3 during manufacture of the cap, the main charge 5 can be pressed in its place with more force than the ignition charge 4, or vice versa.

The desired degree of sensitivity of the cap or initiating means is prirnally determined by the nature of the material of the pin 2 and anvil 3. If both are of steel the sensitivity is relatively low though sufficient for ignition of the ignition charge. At the same time the steel anvil prevents an uncontrolled (in respect of initiation times) explosion deep in the ignition charge. If a steel pin is used with a glass anvil the layer of the ignition charge 4, 4a on the anvil being dextrinated lead azide of a thickness of 0.5 mm., the impact energies are between 800 and 1000 millimetre-grams, While a glass pin on striking a steel anvil under analogous conditions would result in an impact energy of from 300 to 400 millimetre-grams. If both pin and anvil are of glass, the conditions being the same, detonation is certain at impact energies as low as 200 millimetre-grams. The sensitivity can be further improved by mat-grinding the glass faces to increase friction on impact. Besides ordinary steel other metallic materials such as brass, stainless steel and sinter metals can be used. Instead of glass flint and ceramic materials can be used.

The sensitivity of the percussion cap may be further influenced, though to a less degree, by the thickness of the layer 4 on the anvil, the sensitivity increasing with reduced thickness of layer. The necessary impact energy is reduced due to reduced loss of energy on account of the penetration and reduced path of the pin. In all circumstances it is important that the detonation or deflagration should occur on the surface of the anvil which limits the maximum permitted thickness of the ignition layer.

In use the pin 2 is moved against the percussion cap and the anvil 3 or vice versa. The protective foil 6 and the ignition layer 4 on the anvil are first pierced. The frictional heat developed between the pin and the ignition charge 4 is not suflicient to initiate this ignition charge 4 owing to the slight thickness of the layer 4, so that the danger of detonations taking place at a shorter time than the desired initiation time will be eliminated. The actual defiagration is started by the direct impact of the pin 2 on the anvil 3. In the example given with impact of steel against steel, the heat development is utilized while if a glass element is used the heat of splintered-off glass particles on impact plays an important role for distributing the heat energy on impact in the ignition charge. Probably particles are thrown out from the impact zone into the ignition charge at a high velocity.

Without reducing the safety of operation the construction can be used with a transition from more sensitive ignition charges such as undextrinated lead azide with some tetrazene to less sensitive ones, such as dextrinated lead azide.

The anvil 3 can be provided with a thin collar or be fixed to an anchoring foil placed in the surface between the main or intermediate charge 5 and the ignition charge 4 to maintain the anvil in its position in the percussion cap during manufacture and also during use.

In the embodiment according to FIGURE 2 the anvil 3 is shaped so as to secure efliciently that the anvil is maintained in its place in the capsule even when subjected to great acceleration or vibration. This shape also facilitates manufacture of the capsule in small sizes. The anvil 3 here forms a barrier between two layers of the charges 4a and 4b of which a thin ignition layer 4a has been applied to one face of the anvil surface while a thicker priming charge layer 4b supports the anvil 3 and engages the main charge 5. Thus, the anvil 3 can be rigidly secured in the capsule 1 of the cap. Besides serving as an impact element the anvil 3 in this case serves to transmit an explosive impulse to the underlying priming charge 4b. The anvil 3 and the pin 2 can be made of steel or glass, for instance, according to the desired impact sensitivity.

Although the embodiments show anvils lying in or forming boundary surfaces between charges or explosive mixtures of difierent kinds it is, of course, also possible to embed the anvil wholly in the ignition charge or primer. The invention is not restricted to the embodiments shown but can also be modified within the scope of the following claims.

What we claim is:

1. Means for initiating an encapsulated igniter primer comprising in combination, an anvil with flat upper and lower surfaces, a thin layer ignition charge pressed onto said anvil and substantially coextensive in area with the upper surface thereof, the coextensive areas of said ignition charge and said upper surface being in surface to surface contact throughout, a priming charge contacting and substantially coextensive in area with the lower surface of the anvil, the coextensive areas of said priming charge and said lower surface being in surface to surface contact 7 throughout, a pin arranged upon striking to penetrate the made of a metallic material and the pin is made of glass.

4. Means according to claim 3 wherein said pin has a point which has matted unpolished, roughened surfaces of a degree of roughness sufiicient to increase the impact sensitivity by increasing the friction on impact at said an Vil surface.

5. Means according to claim 1 wherein the anvil is made of glass and the pin of a metallic material.

6. Means according to claim 5 wherein said surface of the anvil carrying said thin explosive layer is matted to a degree of roughness sufficient to increase the impact sensitivity by increasing the friction on impact.

7. Means according to claim 1 wherein both the anvil and the pin are made of metallic material.

8. Means according to claim 1 wherein the anvil forms a complete partition Wall in the form of a barrier between the ignition charge and the priming charge.

References Cited in the file of this patent UNITED STATES PATENTS 170,780 Smoot Dec. 7, 1875 183,925 Hobbs Oct. 31, 1876 1,333,496 Knight Mar. 9, 1920 2,068,516 Seavy Jan. 19, 1937 2,361,955 Moore et a1. Nov. 7, 1944 2,398,718 Rasmussen Apr. 16, 1946 FOREIGN PATENTS 13,768 Great Britain 1885 378,769 Germany Aug. 1, 1923 

1. MEANS FOR INITIATING AN ENCAPSULATED IGNITER PRIMER COMPRISINGD IN COMBINATION, AN ANVIL WITH FLAT UPPER AND LOWER SURFACES, A THIN LAYER IGNITION CHARGE PRESSED ONTO SAID ANVIL AND SUBSTANTIALLY COEXTENSIVE IN AREA WITH THE UPPER SURFACE THEREOF, THE COEXTENSIVE AREAS OF SAID IGNITION CHARGE AND SAID UPPER SURFACE BEING IN SURFACE TO SURFACE CONTACT THROUGHOUT, A PRIMING CHARGE CONTACTING AND SUBSTANTIALLY COEXTENSIVE IN AREA WITH THE LOWER SURFACE OF THE ANVIL, THE COEXTENSIVE AREAS OF SAID PRIMING CHARGE AND SAID LOWER SURFACE BEING IN SURFACE TO SURFACE CONTACT THROUGHOUT, A PIN ARRANGED UPON STRIKING TO PENETRATE THE CAPSULE AND SAID IGNITION CHARGE AND TO STRIKE THE UPPER FLAT SURFACE ANVIL TO THEREBY DETONATE THE IGNITION CHARGE AT SAID UPPER FLAT SURFACE. 